Broad-based research is continuing into the creation of a network such as an internet and a ubiquitous network capable of communication at all times and from all places.
The present applicant has carried out research into techniques of seamless handover between heterogeneous wireless networks (Non Patent Literature 1 and 2) and research into software wireless techniques enabling connection with heterogeneous wireless interfaces to switch the wireless systems (Non Patent Literature 3).
Currently since mobile communication terminals such as personal digital assistants (PDA), mobile phones or small laptop computers are provided with a plurality of wireless communication methods, a user can perform wireless communication by switching and selecting an optimal system from the plurality of systems or can increase the communication speed by using more than one method at the same time.
On the most practical level, it is often the case that different data communication devices must be used depending on the respective methods or wireless network providers.
For example, it is sometimes the case that one wireless network provider provides a data communication device using a USB interface and another network provider provides a data communication device using a PCMCIA interface.
When switching between heterogeneous types of wireless communication networks, even when using the same type of wireless network, naturally a relatively long period of time is required to scan the network of different channels and execute a connection.
That is to say, in contrast to wireless communication networks such as those for mobile telephones in which base stations are arranged in a planned manner, networks such as wireless LANs in which all base station positions are not always identified require scanning by a communication terminal to enable switching communication to other networks and channels.
However when a communication terminal moves between base stations, the scanning of the connection-destination network or connection processing may not be performed in a timely manner resulting in the problem that the connection is cut off or communication quality is adversely affected.
Furthermore when scanning all networks or channels enabling communication in a communication terminal, the battery residual charge is reduced by the consumption of a large amount of power thereby adversely affecting the speed of other process due to the scanning process.
Patent Literature 1 discloses a technique which is a conventional patent technique related to the above problem. This technique has the object of avoiding unnecessary scanning operations when there is no prospect of detecting a base station enabling communication and thereby enabling extension of the usable life of a battery by reducing power consumption.
As a result, when an access point enabling communication cannot be detected, in the event that there is no change in the access points detected by the current scan from the scan on an immediately previous occasion and the fluctuation in reception signal intensities from the detected access points are all within a permissible range, it is determined that the local terminal STA1 is in a state of standstill.
In this case, only the access point with the highest reception signal intensity is set as the tracking target and during a subsequent interval, scanning is only performed with respect to the wireless channel for the unique access point set as the tracking target.
Although this method prevents unnecessary scanning operations when the local terminal is in standstill, it cannot be adapted when the terminal is migrating and furthermore entails the problem that reception signal intensity must be constantly measured.